Multiscale creep compliance of epoxy networks at elevated temperatures

Abstract

Epoxy networks are thermoset polymers for which an important structural length scale, molecular weight between crosslinks (M c), influences physical and mechanical properties. In the present work, creep compliance was measured for three aliphatic epoxy networks of differing M c using both macroscale torsion and microscale depth-sensing indentation at temperatures of 25 and 55°C. Analytical relations were used to compute creep compliance (J (t)) for each approach; similar results were observed for the two techniques at 25°C, but not at 55°C. Although creep compliance measurement differed at elevated temperatures, there were clear correlations between M c, glass transition temperature, T g, and the observed time-dependent mechanical behavior via both techniques at 55°C, but these correlations could not be seen at 25°C. This work demonstrates the capacity of depth-sensing indentation to differentiate among epoxy networks of differing structural configurations via J (t) for small material volumes at elevated temperatures. © Society for Experimental Mechanics 2007.